Problems Description
<p class="p0" style="text-indent:21.0000pt;text-align:justify;vertical-align:;"> <span style="font-size:11.0000pt;font-family:'微软雅黑';">在ACM的世界里有一种非常不稳定的原子，叫做</span><span style="font-size:11.0000pt;font-family:'微软雅黑';">β原子，这种原子的贮存有很多限制，他们必须横向排列在一items专用的管problems内，每一itemsβ原子都有左右两items相邻的β原子（头尾除外），β原子有一种属性叫做震荡值，两items相同震荡值的β原子相邻的话，这两itemsβ原子就会相互碰撞，最后两itemsβ原子都会湮灭。起初所有的β原子处于沉睡状态，当你通电后，他们就处于活跃状态，和相邻的原子发生反应。你的任务就是，看看这一排β原子在经过有限次相邻原子交换后是否可以通电（通电后他就会和周围相同震荡值的原子发生反应，我们为了避免反应，就不会通电）</span><span style="font-size:11.0000pt;font-family:'微软雅黑';"></span> </p>
Input格式
<p class="p0" style="text-indent:21.0000pt;text-align:justify;vertical-align:;"> <span style="font-size:11.0000pt;font-family:'微软雅黑';"> Page 一行一items整数N，代表接下来有N（1 </span><span style="font-size:11.0000pt;font-family:'Arial';">≤</span><span style="font-size:11.0000pt;font-family:'微软雅黑';"> N </span><span style="font-size:11.0000pt;font-family:'Arial';">≤</span><span style="font-size:11.0000pt;font-family:'微软雅黑';"> 100</span><span style="font-size:11.0000pt;font-family:'微软雅黑';">）items</span><span style="font-size:11.0000pt;font-family:'微软雅黑';">β原子</span><span style="font-size:11.0000pt;font-family:'微软雅黑';"></span> </p> <p class="p0" style="text-indent:21.0000pt;text-align:justify;vertical-align:;"> <span style="font-size:11.0000pt;font-family:'微软雅黑';"> Page 二行Nitems整数（a</span><span style="font-size:11.0000pt;font-family:'微软雅黑';vertical-align:sub;">1</span><span style="font-size:11.0000pt;font-family:'微软雅黑';">, a</span><span style="font-size:11.0000pt;font-family:'微软雅黑';vertical-align:sub;">2</span><span style="font-size:11.0000pt;font-family:'微软雅黑';">, a</span><span style="font-size:11.0000pt;font-family:'微软雅黑';vertical-align:sub;">3</span><span style="font-size:11.0000pt;font-family:'微软雅黑';">, .........a</span><span style="font-size:11.0000pt;font-family:'微软雅黑';vertical-align:sub;">n</span><span style="font-size:11.0000pt;font-family:'微软雅黑';">)表示每items原子的震荡值（1 </span><span style="font-size:11.0000pt;font-family:'Arial';">≤</span><span style="font-size:11.0000pt;font-family:'微软雅黑';"> a</span><span style="font-size:11.0000pt;font-family:'微软雅黑';vertical-align:sub;">n</span><span style="font-size:11.0000pt;font-family:'Arial';">≤</span><span style="font-size:11.0000pt;font-family:'微软雅黑';"> 1000</span><span style="font-size:11.0000pt;font-family:'微软雅黑';">）</span><span style="font-size:11.0000pt;font-family:'微软雅黑';"></span> </p>
Output格式
<p class="p0" style="text-indent:21.0000pt;text-align:justify;vertical-align:;"> <span style="font-size:11.0000pt;font-family:'微软雅黑';">如果可以通电输出“YES”， 不可以输出“NO”（没有双引号）</span><span style="font-size:11.0000pt;font-family:'微软雅黑';"></span> </p>
Sample
Sample Input 1
3
1 1 2
4
7 7 7
Sample Output 1
YES
NO
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